1. Field of the Invention
The present invention relates to an improved continuously variable transmission system which incorporates therein a toroidal type continuously variable transmission in addition to a gearwheel type transmission (such as using a planetary gear mechanism) for use as a vehicular automatic transmission. The present invention improves the characteristics of a vehicle at a start thereof, as well as prevent an excessive reduction in speed of the vehicle even though a gearshift is operated while running.
2. Description of the Background Art
It is known that toroidal type continuously variable transmissions which are used as automotive automatic transmissions are described in many publications including 1) Japanese Patent Unexamined Publication JP-A-2001-317601, 2) “Best Car Supplement Volume entitled Red Badge Series 245/Book Presenting Automotive Latest Mechanisms” pp. 92-93 written by Motoo Aoyama, and published by Kabushiki Kaisha San Yuh Sha/Kabushiki Kaisha Kodansha, on Dec. 20, 2001, and 3) “Toroidal CVT” written by Hirohisa Tanaka and published by Kabushiki Kaisha Corona on Jul. 13, 2000 and the like and some of them are actually put in practical use. A toroidal type continuously variable transmission like this includes an input disk and an output disk of which respective facing axial side surfaces are made into a toroidal surface and which are supported concentrically with each other in a relatively rotatable fashion and a plurality of power rollers which are held between the input side and output disks. When in operation, the rotation of the input disk is transmitted to the output disk via the individual power rollers. The power rollers are rotatably supported on support members such as trunnions, respectively. The support members are supported in such a manner as to freely swing to be displaced about pivot shafts, respectively, which are situated at positions turned relative to a center axis of both the disks. When attempting to change a gear ratio between the disks, the support members are displaced in an axial direction of the pivot shafts by means of an hydraulic actuator, respectively. The supply and discharge of pressure oil to and from the actuator like this is controlled by a gear ratio control valve, and the movement of the support members is fed back to the gear ratio control valve.
When the support members are displaced in the axial direction of the pivot shafts based on the supply and discharge of pressure oil to and from the actuator, the direction of a tangential force acting on a rolling contact portion (a traction portion) between respective circumferential surfaces of the power rollers and the respective side surfaces of the input side and output disks is changed (a side lip is generated on the rolling contact portion). Then, the individual support members swing (tilt) about the corresponding pivot shafts in association with the change of the direction of the force. Contact positions are changed accordingly where the circumferential surfaces of the power rollers and the side surfaces of the input side and output disks are in contact with each other. When the circumferential surfaces of the power rollers are brought into rolling contact with a portion on the side surface of the input disk which lies radially further outwards and a portion on the side surface of the output disk which lies radially further inwards, the gear ratio between the two disks is changed to a speed increasing side. In contrast to this, when the circumferential surfaces of the power rollers are brought into rolling contact with a portion on the side surface of the input disk which lies radially further inwards and a portion on the side surface of the output disk which lies radially further outwards, the gear ratio between the two disks is changed to a speed decreasing side.
In addition, when the toroidal continuously variable transmission that has been described above is attempted to be installed in an actual vehicular automatic transmission, there has been conventionally proposed a configuration in which the toroidal type continuously variable transmission is combined with a gearwheel type differential unit using a planetary gear mechanism or the like to make up a continuously variable transmission system. For example, Japanese Patent Unexamined Publications No.JP-A-2003-307266 describes a continuously variable transmission system utilizing a so-called Geared Neutral (GN) construction in which with an input shaft kept rotating in one direction, the rotating state of an output shaft can be switched between forward rotation and reverse rotation across a stationary state. In the case of the continuously variable transmission system like this, a torque which passes through the toroidal type continuously variable transmission needs to be controlled in such a state that the output shaft is stopped or is allowed to rotate at extremely low speed with the input shaft kept rotating. In view of this situation, Japanese Patent Unexamined Publication No.JP-A-2004-225888 describes a control method for controlling the torque that passes through the toroidal type continuously variable transmission (which is called as through torque) to a target value by, while roughly controlling the rotational speed of an engine which drives the input shaft, adjusting the gear ratio of the toroidal type continuously variable transmission in accordance with the rotational speed of the so controlled engine.
In addition, it is described in the JP-A-2004-225888 that the gear ratio of the toroidal type continuously variable transmission is adjusted (corrected) so that a torque (a driving force, a creeping force), which somehow enables a vehicle to start from a rest state and run at low speed in a traveling direction, can be transmitted to the output shaft in such a state that the output shaft is stopped with the input shaft kept rotating (an infinite gear ratio state of the continuously variable transmission system=a GN state of the toroidal type continuously variable transmission). To describe specifically, it is described that for an example, when the gearshift is shifted from a non-running state such as a P range (a parking position) or an N range (a neutral position) to a running state such as a D range (a normal forward position), an L range (a forward position with high driving force) or an R range (a reverse position) with the vehicle stopped, the gear ratio of the toroidal type continuously variable transmission is adjusted so that a torque that is outputted from the continuously variable transmission system (a torque that is transmitted to the output shaft) becomes a predetermined value which corresponds to the respective positions (D, L, R) to which the gearshift is shifted (for example, a value at which a torque is obtained which somehow enables the vehicle to start from rest and run at low speed in the traveling direction) on a condition where the depression of the brake pedal is released.
Additionally, Japanese Patent Unexamined Publication No. JP-A-2004-308853 describes an invention relating to a continuously variable transmission which can strictly control a gear ratio of a toroidal type continuously variable transmission so that a torque applied to an output shaft becomes nil or is reduced to a small value. FIGS. 15 to 16 show the continuously variable transmission system described in the JP-A-2004-308853. FIG. 15 shows a block diagram of the continuously variable transmission system. In FIG. 15, a thick arrow denotes a power transmission path, a solid line denotes a hydraulic circuit, and a broken line denotes an electric circuit. An output from an engine 1 is inputted into an input shaft 2 via a damper 2. Power transmitted to the input shaft 3 is transmitted from a hydraulic pressurizing device 5, which makes up a toroidal type continuously variable transmission 4, to an input disk 6 and the power is further transmitted to an output disk 8 via power rollers 7.
In the two disks 6, 8, the rotational speed of the input disk 6 is measured by an input side rotation sensor 9, whereas the rotational speed of the output disk 8 is measured by an output side rotation sensor 10. Respective measured speeds are inputted into a control unit 11 for calculation of a gear ratio (a speed ratio) between the two disks 6, 8 (a gear ratio of the toroidal type continuously variable transmission 4). In addition, the power transmitted to the input shaft 3 is transmitted to a planetary gear type transmission 12, which is a differential unit, directly or via the toroidal type continuously variable transmission 4. Then, a differential component of constituent members of the planetary gear type transmission 12 is taken out to an output shaft 14 via a clutch device 13. This clutch device 13 represents a low-speed clutch 15 and a high-speed clutch 16 shown in FIG. 16 which will be described later on. In addition, an output shaft rotation sensor 17 is able to detect the rotational speed of the output shaft 14.
On the other hand, an oil pump 18 (18a, 18b in FIG. 16) is driven by power taken out from the damper 2 portion, and pressure oil discharged from the oil pump 18 is free to be sent into the pressurizing device 5 and a control valve unit 20 for controlling a displacement amount of an actuator 19 (refer to FIG. 16) for displacing trunnions, which are support members for supporting the power rollers 7 in an axial direction of pivot shafts (not shown). Note that this control valve unit 20 is made up of a combination of a gear ratio control valve 21, a differential pressure cylinder 22, correcting control valves 23a, 23b, a high-speed switching valve 24 and a low-speed switching valve 25 which are shown in FIG. 16 for a subsequent description. In these constituent members, the gear ratio control valve 21 controls the supply and discharge of pressure oil to and from the actuator 19. In addition, oil pressures in a pair of hydraulic chambers 26a, 26b (refer to FIG. 16) provided in the actuator 19 are detected by an oil pressure sensor 27 (actually, a pair of oil pressure sensors 27a, 27b as shown in FIG. 16), and detection signals are inputted into the control unit 11.
The control unit 11 calculates a torque that passes through the toroidal type continuously variable transmission 4 (the through torque) based on signals from the oil pressure sensor 27. Then, in order to correct the gear ratio of the toroidal type continuously variable transmission 4 according to the so calculated through torque, a sleeve 28 (refer to FIG. 16) which is a constituent member of the gear ratio control valve 21 is displaced by the differential pressure cylinder 22. The supply and discharge of pressure oil to and from the differential pressure cylinder 22 like this is controlled by the correcting control valves 23a, 23b. In addition, the operating state of the control valve unit 20 is switched by a stepping motor 29, a line pressure control solenoid switch valve 30, a solenoid valve 31 for switching the correcting control valves 23a, 23b and a shifting solenoid valve 32 for switching the high-speed switching valve 24 and the low-speed switching valve 25. In addition, any of the stepping motor 29, the line pressure control solenoid switch valve 30, the solenoid valve 31 and the shifting solenoid valve 32 is switched based on a control signal from the control unit 11.
In addition to signals from the individual rotation sensors 9, 10, 17 and the oil pressure sensor 27, a detection signal from an oil temperature sensor 33, a position signal from a position switch 34, a detection signal from an accelerator sensor 35 and a detection signal from a brake switch 36 are inputted into the control unit 11. Among the sensors, the oil temperature sensor 33 detects temperature of lubricating oil (traction oil) which resides within a casing which accommodates therein the continuously variable transmission system. The position switch 34 generates a signal representing an operation position (a selected position) to which a gearshift (an operation lever), which is provided in the vicinity of a driver's seat, is operated for switching a manual oil pressure switching valve 37 shown in FIG. 16, which will be described later on. Additionally, the accelerator sensor 35 detects the opening of an accelerator pedal. Furthermore, the brake switch 36 detects the depression of the brake pedal or the operation of a parking brake and generate a signal which signals the detected fact.
In addition, based on signals from the individual switches 34, 36 and individual sensors 9, 10, 17, 27, 33, 35, the control unit 11 sends the control signals to the stepping motor 29, the line pressure control solenoid switch valve 30, the solenoid valve 31 and the shifting solenoid valve 32 and additionally sends a control signal to an engine controller 38 for controlling the engine 1. Then, as is described in the JP-A-2004-225888, the control unit 11 changes the speed ratio between the input shaft 1 and the output shaft 14, or the control unit 11 controls the torque (the through torque) that passes through the toroidal type continuously variable transmission 4 applied to the output shaft 14 while the vehicle is stopped or runs at extremely low speed. Furthermore, in a case where the JP-A-2004-308853 describes, a rotational speed and rotational direction of the output shaft 14 are calculated for controlling the through torque.
FIG. 16 shows the hydraulic circuit controlling the continuously variable transmission system as described above. In this hydraulic circuit, pressure oil, which is sucked from an oil reservoir 39 to be discharged by the oil pumps 18a, 18b, is made free to be adjusted to a predetermined pressure by means of pressure regulator valves 40a, 40b. In these pressure regulator valves 40a, 40b, pressure regulated by the pressure regulator valve 40a for regulating an oil pressure sent to the manual oil pressure switching valve 37 side is made free to be regulated based on the opening or closing of the line pressure control solenoid switch valve 30. Then, pressure oil whose pressure is regulated by both the pressure regulator valves 40a, 40b is made free to be sent into the actuator 19 via the gear ratio control valve 21 and is also made free to be sent into the correcting control valves 23a, 23b for adjusting the stroke of the differential pressure cylinder 22 based on the opening or closing of the solenoid valve 31. In addition, the pressure oil is also made to be sent into the hydraulic pressurizing device 5.
In addition, this pressure oil is made free to be sent into the hydraulic chamber of the low-speed clutch 15 or the high-speed clutch 16 via the manual oil pressure switching valve 37 and the high-speed switching valve 24 of the low-speed switching valve 25. Additionally, in these low-speed clutch 15 and the high-speed clutch 16, the low-speed clutch 15 is engaged when realizing a low-speed mode in which a reduction ratio is increased (including an infinite gear ratio) and is disengaged when realizing a high-speed mode in which the reduction ratio is decreased. In contrast to this, the high-speed clutch 16 is disengaged when realizing the low-speed mode and is engaged when realizing the high-speed mode. In addition, the supply and discharge of pressure oil to and from these low-speed and high-speed clutches 15, 16 is selected according to the switching state of the shifting solenoid valve 32.
In the case of the invention described in the JP-A-2004-308853, the rotational speed and rotational direction of the output shaft 14 are calculated based on the detection signals of the input side rotation sensor 9 and output side rotation sensor 10 in the manner described above, so as to control the through torque of the toroidal type continuously variable transmission 4. Accordingly, the gear ratio of the toroidal type continuously variable transmission can be strictly controlled so that the torque applied to the output shaft becomes nil or falls to a small value in the non-running state. In addition, even when the gearshift is operated from the non-running state to the running state, the predetermined driving force (the driving force which somehow enables the vehicle to start from a rest state and run at low speed in the traveling direction) is made to be outputted from the output shaft.
In addition, Japanese Patent Examined Publication JF-B-3460676 describes an invention which prevents the occurrence of a case where when a gearshift is operated from a non-running state to a running state, a predetermined torque cannot be outputted from an output shaft of a continuously variable transmission system based on a torque shift. Namely, in an event that a torque that passes through a toroidal type continuously variable transmission which makes up the continuously variable transmission system fluctuates in such a state that a gear ratio of the toroidal type continuously variable transmission is adjusted to the vicinity of a value (a GN value) at which a state can be realized where an output shaft is stopped with an input shaft kept rotating, a torque shift where the gear ratio of the toroidal type continuously variable transmission fluctuates is generated due to inevitable elastic deformation of individual constituent members and/or assembling clearance. Then, when the torque shift like this occurs, even in the event that a stepping motor for changing the switching state of a gear ratio control valve for controlling the gear ratio of the toroidal type continuously variable transmission is driven to a predetermined position such as a position where the state can be realized in which the output shaft is stopped with the input shaft kept rotating (a position where a GN state can be realized), there occurs a possibility that the gear ratio of the toroidal type continuously variable transmission is caused to deviate from a gear ratio which corresponds to the position of the gearshift is operated.
When there occurs such a deviation in the gear ratio of the toroidal type continuously variable transmission, there occurs a possibility that the output shaft cannot be stopped or a predetermined driving force cannot be outputted from the output shaft. In order to prevent the occurrence of such inconvenience, in the case of the invention described in the JP-B-3460676, when the gearshift is operated from the non-running state to the running state, after the stepping motor has been temporarily driven in a predetermined direction (a direction in which it is separated away from the position where the GN state can be realized) which corresponds to a position to which the gearshift is operated (the running state), the stepping motor is driven to the predetermined position where the GN state can be realized. As a result, irrespective of the occurrence of the aforesaid shift torque, the gear ratio of the toroidal type continuously variable transmission can be accurately adjusted to a desired value, so that the output shaft can be stopped, or the predetermined driving force can be outputted from the output shaft.
Additionally, Japanese Patent Unexamined Publication No.JP-A-2002-89669 describes an invention which prevents the occurrence of a halt of an engine when a gearshift is operated from a non-running state to a running state whether or not a brake pedal is depressed. Namely, when the gearshift is operated from the non-running state to the running state, in an event that a gear ratio of a toroidal type continuously variable transmission is simply attempted to be adjusted to a value at which a driving force in a traveling direction can be outputted from an output shaft in such a state that the brake pedal is depressed, depending upon the magnitude of the driving force so outputted, an excessive load is applied to the engine, leading to a possibility that the engine is stopped. In order to prevent the occurrence of such inconvenience, in the case of the invention described in the JP-A-2002-89669, when the gearshift is operated from the non-running state to the running state, a stepping motor for changing the switching state of a gear ratio control valve for controlling the gear ratio of the toroidal type continuously variable transmission is driven as will be described below.
Namely, the stepping motor is driven within a range where the gear ratio of the toroidal type continuously variable transmission can fall to a value at which the gear ratio can become the GN value based on the torque shift without stopping the engine and in such a manner that the gear ratio can become a value at which a necessary driving force in the traveling direction can be outputted from the output shaft. As a result, a state can be realized where when the gearshift is operated from the non-running state to the running state, even with the brake pedal depressed, the output shaft can be stopped with the input shaft kept rotating in one direction due to the gear ratio being changed to the GN value based on the toque shift. In addition, in association with this, irrespective of the fact that a load based on the torque shift is applied to the engine, the engine can be prevented from being stopped. In addition, the depression of the brake pedal is released from the state where the output shaft is stopped based on the depression of the brake pedal like this, the vehicle can be started in a smooth fashion.
Incidentally, in the case of the inventions that are described in the JP-B-3460676 and JP-A-2002-89669, respectively, the following points are not taken into consideration. Namely, in the case of the inventions described in the JP-B-3460676 and JP-A-2002-89669, when the gearshift is operated from the non-running state to the running state, even though the gear ratio of the toroidal type continuously variable transmission is adjusted (corrected) to the predetermined value by driving the stepping motor in the way described above, there exists a possibility that the clutch device for switching the power transmitting state is engaged before the gear ratio has reached (has been corrected completely) to the predetermined value. As this may occur, the vehicle is likely to exhibit a behavior that the driver does not intend, which is not preferable. For example, when the driver attempts to shift the gearshift from the non-running state to the running state to start the vehicle in a selected direction immediately, a torque in the intended direction cannot be outputted from the output shaft, leading to a possibility that the driver cannot start the vehicle from rest in the intended direction. In addition, when the gearshift is operated, for example, from the D range to the R range without depressing the brake pedal, there exists a possibility that the vehicle moves forwards even momentarily irrespective of the gearshift being shifted into the R range.
In addition, in the case of the inventions described in the JP-B-3460676 and the JP-A-2002-89669, the operation of the gearshift is detected by a gear selection position detecting device (JP-B-3460676) or a start selection detecting device (JP-A-2002-89669), so that the adjustment of the gear ratio is effected in the way described above based on the detection. Thus, when the adjustment of the gear ratio is carried out after the operation of the gearshift has been detected by the detection devices, there is a possibility that a slippage on timing (a delay in operation) occurs between the gearshift operating timing and a driving timing at which the driving member such as the stepping motor is driven to adjust the gear ratio to the desired value based on the detection by the detection devices. The slippage on timing like this may constitute a cause for a risk where the vehicle behaves in a way that the driver does not intend, which is not preferable to occur.
In addition, in the event of the inventions described the JP-B-3460676 and the JP-A-2002-89669, whenever the gearshift is operated from the non-running state to the running state, the gear ratio is considered to be adjusted to the GN value or the value at which the predetermined driving force can be outputted from the output shaft. Due to this, in the event that the gearshift is shifted to the non-running state (N range) due to an erroneous operation of the gearshift by the driver or an intended one with a view to improving the fuel economy while the vehicle is running and is then shifted back to the non-running state to the running state (D range), there exists a possibility that the gear ratio is adjusted to the GN value or the value at which the predetermined driving force is outputted from the output shaft. As this may occur, the vehicle is likely to be reduced in speed unintentionally excessively, making the driver feel a sensation of physical disorder, which is not preferable to occur.
Additionally, U.S. Pat. No. 6,663,532 describes an invention which controls a torque that passes through a toroidal type continuously variable transmission when a vehicle is started from a rest state. In the case of the invention described in the U.S. Pat. No. 6,663,532, however, until power (torque) is inputted into the toroidal type continuously variable transmission through engagement of a clutch device, the torque that passes through the toroidal type continuously variable transmission cannot be adjusted to a target value which is a value at which a driving force in a traveling direction can be outputted from an output shaft. In other words, there exists a possibility that the clutch device is engaged before the torque that passes through the toroidal type continuously variable transmission is adjusted to the target value so that the clutch device is allowed to transmit power. Due to this, as has been described above, there exists a possibility that the vehicle behaves in the way that the driver does not intend, which is not preferable to occur.